If you get right down to the science of it, love is produced by the part of the brain that is most concerned with the cognition of "trust." Love is therefore a specialized manifestation of the trust impulse. Trust somehow gets translated into the need to protect or preserve something other than oneself. In the evolutionary record, the development of this ability would have signaled the rise of the social animal. Social in a way that was not controlled by simple chemical commands like ants.

Trust is an emotion. An emotion because it is governed by a part of the brain that possesses no capacity to reason and therefore cannot be a product of our intelligence. It's counterpart is fear. Also produced in the same region, but not the same structure. Fear is likely older than trust, as the mechanism for fear, the amygdala is thought to biologically predate the formation of the mechanisms for love in the limbic region of the brain. Fear is also an emotion.

Trust and fear, however, are different than the other emotions produced in the limbic system. With the higher emotions like anger, jealousy, sadness, happiness, the emotion exists prior to its physical affects on the body. However, with trust and fear, or love, the emotion and its physical affects on the body occur simultaneously. As if in their case, there is no difference between physical and mental states.

So to say that love was either emotion or physical impulse would be erroneous either way. Love is obviously something that exists across the mind/body boundaries. It's more primitive and pervasive than the higher mind functions.